1. Field of the Invention
The present invention relates to an apparatus and method of controlling injection in an electric injection molding machine, and more particularly to an apparatus and method of controlling injection in an electric injection molding machine in which the number of control loops is minimized upon operation of the injection molding machine to thereby reduce a loop time and a scanning time in the control process and make a production rate of an injection molding product speedy.
2. Description of the Prior Art
Generally, an electric injection molding machine of the prior art, as shown in FIG. 1, includes a barrel 11, a screw 12, a motor 20, an encoder 21, a main controller 22, a velocity controller 23, a current controller 24, a velocity converter 25, and a power converter 26.
The barrel 11 is a portion to which a resinous solution is injected. The screw 12 is connected with the motor 20 so as to move back and forth in the barrel through rotation.
A structure that the barrel 11 and the screw 12 are combined with each other is called an injection shaft. When the screw 12 in the barrel 11 is moved back and forward by rotating motion of a ball screw 15 according to a drive of the motor 20, a pressure is generated in the barrel 11 so that the resinous solution can be injected.
The encoder 21 is connected with the motor 20, the main controller 22, and the velocity converter 25, and the velocity converter 25 and the main controller 22 are connected with the velocity controller 23. The velocity controller 23 is connected with the current controller 24, which is connected with the power converter 26, which is in turn connected with the motor 20.
The encoder 21 outputs a position of the screw 12 according to a drive of the motor 20 as an encoding signal.
The velocity converter 25 differentiates and converts the encoding signal output from the encoder 21 to velocity data of the screw 12, and transmits the date to the velocity controller 23. For example, the velocity converter 25 is composed of a differentiator.
The main controller 22 transmits, to the velocity controller 23, predetermined velocity data such that the screw 12 moves in a proper velocity. For instance, the predetermined velocity data is input through an input unit (not shown). The input unit is composed of a key input (key pad), for example.
Further, the main controller 22 determines the position of the screw 12 from the encoding signal received from the encoder 21.
The velocity controller 23 compares the velocity data from the velocity converter 25 with the predetermined velocity data from the main controller 22, calculates a rotation velocity of the motor 20 corresponding to the moving velocity of the screw 12, and transmits the calculated data to the current controller 24.
The current controller 24 receives an instruction current value, and conducts a close loop control through measuring the amount of current from the power converter 26 so as to follow the current value. Then, the power converter 26 is driven. The current controller calculates a quantity of power required for the control of rotation velocity of the motor 20 using the data transmitted from the velocity controller 23. Further, the current controller 24 obtains power corresponding to the calculated quantity of power through a current loop, and transmits it to the motor 20 to thereby drive the motor 20.
The power converter 26 switches a power device of a final output terminal with a signal generated from the current controller 24 to thereby apply the instruction current value to the motor.
In such a construction, a method of controlling injection will be described as follows.
First, when the motor 20 is driven, the encoder 21 outputs, as an encoding signal, a position of the screw 12 according to a drive of the motor 20 (step 21). The encoder 21 transmits the outputted encoding signal to the velocity converter 25 and the main controller 22.
Then, the main controller 22 checks the current position of the screw 12 using the encoding signal transmitted from the encoder 21.
Then, the velocity converter 25 differentiates and converts the encoding signal outputted from the encoder 21 to velocity data of the screw 12 (step 22), and transmits the converted current velocity data of the screw 12 to the velocity controller 23.
Then, the velocity controller 23 compares the predetermined velocity data of the main controller with the current velocity data of the screw 12, and calculates an instruction current value of the motor 20 for moving the screw 12 at a proper velocity (step 23). Next, the calculated instruction current value is transmitted to the current controller 24.
Then, the current controller 24 transmits the instruction current value from the velocity controller 23 to the motor 20 via the power converter 26 through the close loop control of current value (step 24).
The motor 20 is driven at a certain rotation velocity according to the amount of the current transmitted from the power converter 26 (step 25).
Next, the encoder 21 outputs the position of the screw 12 according to the drive of the motor 20 as an encoding signal.
That is, the above injection control operation is repeated from the step 21, which is called a velocity loop.
Briefly, in the injection control method in the electric injection molding machine of the prior art, an injection molding velocity, i.e., a moving velocity of the screw in the injection molding machine, is controlled through the main controller 22, the current loop and the velocity loop.
Like this, the injection control in the prior injection molding machine should pass through the velocity controller in front of the current controller, and should also receive an velocity instruction from the main controller 22. That is, two control loops (velocity loop, current loop) should be carried out.
While a control loop has a tendency to increase whole loop time two times as it goes toward outer loop, the main controller 22 generally has a tendency to operate lately relative to a servo driver. Further, the velocity converter 25 comes to need an algorithm for measuring the actual velocity and reducing noises occurring during calculating the velocity from the encoder signal for velocity control. In the prior art, there causes a problem in that a molding time of an injection mold is consumed a lot due to increase in scanning time.
That is, due to the velocity converter 25 and the main controller 22 installed outside, in fact, the control scanning time is increased, and in high velocity and high precision injection, the control is not rapidly reactive to the input from the main controller 22, which are problematic.
Further, in manufacturing a product through the injection control in the prior electric injection molding machine, velocity data of the screw are input differently for each case so that a problem arises in that deviation in quality between products manufactured occurs.